1. Field of the Invention
The disclosed embodiments of the present invention relate to a pulse width modulation (PWM) circuit and a PWM signal generation method, and more particularly, to a PWM circuit and a PWM signal generation method that can have two refresh rates.
2. Description of the Prior Art
In electronic apparatuses, a pulse width modulation (PWM) signal is usually utilized as a control signal. For example, the duty cycle of a PWM signal might be adjusted to control the brightness of video frames or the charging/discharging of a voltage conversion circuit.
FIG. 1 is a diagram illustrating a conventional PWM signal. PWM signals with different cycles are denoted by PWMa and PWMb, respectively. As shown in FIG. 1, an example of a minimum pulse (1 ns) is illustrated, where PWMa is a PWM signal with a cycle of 256 ns, and PWMb is a PWM signal with a cycle of 512 ns. When the PWM signal is used to control the brightness of video frames, the cycle means the refresh rate. That is to say, a PWM signal with a short cycle has a higher refresh rate, and a PWM signal with a longer cycle has a lower refresh rate in contrary. In addition, a PWM signal has another important characteristic, the resolution. In the example of FIG. 1, the resolution of the PWMa is 1/256, and the resolution of the PWMb is 1/512. That is to say, PWMb could be a control signal with a precision higher than that of PWMa. However, as described above, the refresh rate of PWMb is lower than PWMa, and thus the resolution is inversely proportional to the refresh rate.
Generally speaking, only a single PWM signal of a single dimension (i.e., a single direction) is used in the current control mechanism of the PWM signal. Therefore, there would be a trade off between the resolution and the refresh rate, thus adding limitations to the circuit design.